Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Other components commonly used include seal sections and gearboxes. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.
Keeping internal areas of the components free of the corrosive well fluids is both important and difficult in the downhole environment. Rotating shafts are commonly used in submersible pumping systems to transfer rotational energy from the motor to the pump assembly. Unfortunately, shafts provide a leak path for the corrosive well fluids to migrate into the components. It is difficult for a seal to effectively block the leak paths along a rotating shaft due to the rotation of the shaft.
Mechanical seals are used to keep well fluids from migrating along rotating shafts. Prior art designs typically include elastomer bellows, springs, runners and o-rings that cooperate to impede the migration of well fluids along the shaft. However, limitations in the present designs result in failures in the mechanical seal that allow well fluids to penetrate undesirable locations and to require costly repairs.
Mechanical seals that include an elastomer bellows have design limitations for applications that undergo axial movement of the shaft. This movement of the shaft can occur during pump starting conditions as a result of pump thrust. The axial movement can cause components of the mechanical seal to move relative to each other, thereby allowing fluid to leak past the seal.
Elastomer bellows in mechanical seals also are disadvantageous for varying depths and conditions of wells. Unique elastomer compounds are frequently needed for different characteristics encountered in a well, such as varying temperatures and corrosive chemical presence. Molding new bellows from alternative elastomers is time consuming and requires expensive tools.
Some mechanical seal designs do not use bellows along the rotating shaft, and instead use o-rings along the shaft. These designs typically use a spring to directly compress the o-ring against a runner and the shaft, thereby sealing the shaft and providing friction to hold the runner adjacent the shaft. Although this design permits axial movement of the shaft without losing the sealing capability of the mechanical seal, any damage to the o-ring may permit the runner to rotate on the shaft and cause the o-ring to fail. While this arrangement eliminates the problems associated with the bellows, it is not as robust as mechanical seals with bellows.
There is therefore a continued need for a mechanical seal for use with a pumping system that prevents leaks along the rotating shaft, eliminates problems associated with the bellows, allows axial movement of the shaft without seal failure, and prevents rotation of the runner relative to the shaft. It is to these and other deficiencies and requirements in the prior art that the present invention is directed.